Structural characterization of thin GaN epilayers directly grown on on-axis 6H-SiC(0001) by plasma-assisted molecular beam epitaxy

The structural properties of a series of thin (0.2-0.6 mu m) GaN epilayers directly grown on 6H-SiC(0001) by plasma-assisted molecular beam epitaxy ar e studied. X-ray reciprocal space maps of the GaN(0002) reflection reveal n egligible inhomogeneous strain within the layer but a comparatively large o rientational spread of the GaN c axis. X-ray rocking curve measurements sho w, however, that this mosaicity steadily decreases with film thickness. In fact, the density of threading defects detected by transmission electron mi croscopy is found to decrease drastically with the distance away from the G aN/SiC interface, finally reaching a value of less than 5 X 10(9) cm(-2) at a layer thickness of 0.5 mm. The formation mechanisms of the threading dis locations in the GaN films are discussed in consideration of the specific G aN/SiC interface structure. (C) 1998 American Institute of Physics. [S0003- 6951(98)05052-9].